MySQL只用MySQL获得结果

Question

Say I had a MySQL table as pictured below, and I wanted to find any product_id 's which have the filters 2 AND 5 (so in the table this would be the product_id of 30), is this possible in MySQL? Or would I have to get product id's where the filter_id is 2 OR 5, and sort it in PHP?

Answer 1

SELECT product_id, COUNT(*) AS i FROM mytable WHERE filter_id IN (2,5) GROUP BY product_id HAVING i = 2;

This will match any rows containing any of the required filter_ids and group together those with the same product_id. The name i has been given to a column giving the number of rows in the group. Assuming that every combination of product_id to filter_id will be unique then you know that any group with two rows will have matched both of the filter_ids, so the HAVING clause will finally filter out the rows that only matched one of the filter_ids.